The patterns of extrinsic connections of the two nuclear subdivisions of the primate neostriatum suggest that the putamen and caudate nucleus may subserve different functions, with the putamen participating principally in motor control while the caudate nucleus is involved in more complex behavioral processes. The studies proposed will examine the degree to which the neostriatum is functionally differentiated, and attempt to clarify some of the mechanisms by which this structure projects its influences to other brain regions via the output nuclei of the basal ganglia (in particular, the internal segment of the globus pallidus (GPi)). The specific aims of the project are: 1) To examine, using single cell recording and microstimulation techniques, the hypothesis that the putamen participates in the preparation for and execution of instruction-dependent motor responses. 2) To examine, using single cell recording techniques, the hypothesis that the audate nucleus is functionally differentiated in accordance with the topographic distribution of its heterogeneous cortical inputs, and thus may have a role a) in the spatial memory processes required for certain instruction-dependent motor responses, and b) in the programming (and possibly execution) of saccadic eye movements in an instruction-dependent visual tracking task. 3) To determine whether the putamen and caudate nucleus have unique and dissociated roles in the motor and more complex behavioral functions which underly instruction-dependent motor responses, by comparing the effects of fiber-sparing neurotoxic (ibotenic acid) lesions of each of these structures on task performance. 4) To determine whether normal movements, as well as those evoked by putamen microstimulation, depend upon GABA-mediated transmission through the output nuclei of the basal ganglia, by characterizing the influence of GPi injections of GABA-related drugs on both types of motor activity. These studies are designed to elucidate the roles of the putamen and caudate nucleus in normal motor and more complex behavioral processes, and should also provide insight into basic mechanisms underlying certain disorders of movement and high-level motor control in patients with diseases of the basal ganglia, including Parkinson's and Huntington's diseases.